The present invention relates generally to multiple order gradiometers and more particularly, to such gradiometers which have heavy, bulky and costly components associated therewith.
Magnetic fields are commonly measured using either a magnetometer or a gradiometer. A magnetometer is an instrument which measures magnetic field intensity in direct proportion to the sensitivity of a single sensing element and therefore, provides no magnetic field background or noise rejection. Various types of magnetometers are known, such as those which utilize moving and stationary coils, Hall Effect Devices, thin films, fluxgates, magnetic resonance devices, superconducting devices and as disclosed in U.S. Pat. No. 4,433,291, a magnetostrictive segment on an optical fiber element. A gradiometer is an instrument which measures the difference between the magnetic field intensities at two separate locations, with at least one pair of magnetometers. Therefore gradiometers provide common made background or noise rejection which can be enhanced by increasing the number of magnetometer pairs to increase the order of the gradiometer.
Although multiple order gradiometers which utilize various types of magnetometers are known in the art, where extreme sensitivity is required superconducting quantum interference devices (SQUIDs) are commonly utilized therein. Because such gradiometers must be cooled to cryogenic temperatures, such as with liquid helium, the applications therefor are severely limited due to the greater size, weight and expense thereof. Furthermore, where applications do exist for such gradiometers, difficulties are encountered therewith in regard to balancing and trimming, which is usually only accomplished by successive approximations. Magnetostrictive segments on optical fiber elements have been utilized in first order gradiometers to overcome the problems encountered with SQUIDs, as disclosed in my U.S. Pat. No. 4,644,273.